The proposal develops a hand-held otoscope that uses optical coherence tomography (OCT) to image the tympanic membrane and ossicles behind an intact tympanic membrane. The system is based on spectral Fourier-domain OCT and can measure vibrations of the ossicles (malleus, incus, stapes) of the middle ear on the scale of nm to m amplitude. In Aim 1 we construct and develop a protype of the otoscope testing the performance of the hardware and middle ear analysis software using phantom objects with known vibration. In Aim 2 we use the prototype otoscope to study human temporal bone specimens to investigate ossicular chain 'disorders' by experimental ossicle fixations and disarticulations. Aim 3 is a pilot clinical use in recruited human subjects with normal or pathological middle ear function as assessed by conventional methods. This new otoscope will greatly improve the non-invasive diagnosis of conductive hearing loss. Current practice relies on either indirect assessment of ossicle movement by measuring compliance of the tympanic membrane to sound or pressure, or direct examination after surgically cutting the tympanic membrane to gain access to the ossicles. The OCT otoscope can directly image and measure vibrations noninvasively, without cutting the tympanic membrane. The project will yield an innovative, non-invasive diagnostic instrument capable of localizing the site of conductive hearing loss behind an intact tympanic membrane. The OCT otoscope will facilitate a better understanding of sound conduction in normal, diseased and reconstructed middle ears, allowing clinicians to make more precise pre-surgical diagnosis, to analyze more informatively post-surgical results, and ultimately to develop more effective treatments for patients with conductive hearing loss.